Communication system



Sept. 6,1927.

J. w. HORTON COMMUNICATION SYSTEM Filed Deg. 15, 1925 15m f7 g 7 Mil) A. M. BF,

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awe W flar/m by /Wjz Patented Sept. 6, 1927.

UNITED STATES 1,641,431 PATENT OFFICE.

JOSEPH W. HORTON, OF BLOOMFIELD, NEW JERSEY, ASSIGNOR TO WESTERN ELEC- TRIO COMPANY, INCORPORATED, OF NEW YORK,

YOIBIK.

N. Y., A CORPORATION 01 NEW COMMUNICATION SYSTEM.

Application filed December 15, 1925. Serial No. 75,523.

. This invention relates to communication systems and more particularly to binaural si naling systems.

n binaural signaling systems in wh ch 6 two separate signal currents corresponding to sounds heard by the left ear and right ear respectively, are transmitted as modula-' tions of carrier waves; it is desirable to confine the transmission channel to a fre- 10 quency range not greater than that occupied by the two side bands, which are produced when a carrier wave is modulated by a single signal current.

It has heretofore been proposed to accomplish this by separately modulating a single carrier wave with two versions of a signal and selecting for transmission the upper side band of one modulation and the lower side band of the other modulation.

In accordance with the present invention two different frequency carrier waves respectively, are modulated by two versions of a signal and one side band selected from each modulation. For radio transmission, the se- 2: lected side bands are then used to modulate a hi h frequency carrier wave and one side ban of this last modulation is selected for transmission.

It is, therefore, an object of this invention to provide a binaural carrier communication system in which a minimum frequency range of the transmission channel is maintained by respectively modulating carrier waves of different frequencies by two versions of a signal.

This object and others .which will be apparent as the nature of the invention is disclosed, are accomplished by modulating two carrier waves of comparatively low but different frequencies by separate versions of the same signal and selecting one side band from each modulation.

When the transmission is to be effected over a radio channel the selected side bands are used to modulate a radio frequency carrier wave. One of the side bands resulting from the last mentioned modulation is selected and used for transmission purposes.

At the receiving station the transmitted 6 wave is combined with current of the frequency of the radio carrier supplied by a local oscillator to produce currents corresponding to the original low frequency side bands which are then selected and separately detected in suitable apparatus to yield the two versions, which are used to actuate a signal responsive means.

Althoiwli the novel features which are believed to be characteristic of this invention will be pointed out with particularity in the claims appended hereto, the invention itself, its ob ects andadvantages, the manner of its organization and the mode of its operation will better understood by referring to the following description taken in connection with the accompanying drawing forming a part thereof in which:

Fig. illustrates diagrammatically a radio transmission system operating in accordance with this invention:

Fig. 2 represents suitable receiving appa-,

ratus adapted to be operated in connection with the transmitter of Fig. 1; and

Fig. 3 is a chart to be usedin explanation of the operation of this system.

Referring more particularly to Fig. 1, the amplitudes of signals received by the two microphones, 1 and 2, are raised to the desired value by suitable amplifiers, A and A respectively, which may consist of any number of stages resired, to increase the amplitude of the impressed currents to the value necessary for modulation.

The amplified iilgnals are then impressed upon modulators 1 and M respectively, in which they are combined with oscillations from oscillators O and O to produce modulation products comprising an unmodulated carrier component and corresponding side band components. The frequency of the oscillations generated by oscillators O and 0 for the purpose of illustration and to completely and clearly disclose a preferred embodiment of this invention, will be assumed to be 15 kc. for oscillator 0 and 25 kc. for oscillator 0 Assuming speech frequency currents to be impressed upon the modulators M and M. from the microphones, the frequency range of the impressed currents will lie, for example, between 0 and 5 kc. This is indicated in Fig. 3 by the two solid lines at the left of the figure extending from the zero axis to the 5 kc. point. The modulation products in the output circuit of modulators M and M respectively, will comprise an unmodulated component of 15 kc. and side band components based thereon, and an unmodulated component of 25 kc..and side bands based thereon. The two modulated products will have frequency ranges such as that illustrated in Fig. 3, namely between 10 kc. and 20 kc., and between 20 kc. and 30 kc., respectively.

The above mentioned modulation products are passed through band pass filters, BF and BF which are respectively adapted to pass the unmodulated carrier component and the upper sideband based on the 15 kc. oscillations, and the unmodulated carrier component and the lower side band based on the 25 kc. oscillations. The side bands and carrier components transmitted through filters BF and BF,, are represented by the full lines in Fig. 3. These products are impressed upon modulator M, by means of transformer 3, wherein they1 are combined with carrier frequency osci ations from oscillator 0,, which are herein assumed to be of the order of 485 kc., although any other carrier frequency suitable for transmission can be used.

A single side band, of the modulation roduots in the output circuit of modulator RI, is selected by band pass filter, BF, and

- impressed upon amplifier A wherein it is amplified to the intensity desired for transmission.

Current in the output circuit of amplifier A is impressed by means of transformer 5 upon a communication channel, which is herein shown as antenna system 4.

Any other type of communication channel, such as that of a transmission line, ma be employed, however, without departing om the spirit of this invention.

The transmitted wave is received in areceiving apparatus by means of energy re ceivmg means, shown as antenna s stem 6 in Fig. 2, and impressed upon demo ulator M wherein it is combined with oscillations roduced by oscillator The frequency 0 the oscillations generated by oscillator O, is

preferably the same or similar to that of the oscillations generated b oscillator 0,, although the operation 0 the system would not be impaired were other frequencies chosen. Assuming, for purposes of illustration, that the oscillator 0 is enerating current'at 485 kc., that is identica with the frequency of oscillator (l, the products of demodulation in the output circuit'of demodulator M will be re resented by the full lines in Fig. 3,- that is, t ey will be identical with the currents impressed upon modulator M, at the transmittin station.

The output of trans ormer 3 may be em plo ed for line transmission if desired, in whlch case modulationand demodulation by a radio frequency carrier will not be requlred. I

, The two carrier currents of 15 and 25 kc.,

respectively, and theirassociated side bands are separated by low pass and high pass filters, HP and LP, and passedthrough amplifiers A and A,,, respectively," wherein they are amplified to the desired intensity. The resulting signals are then detected in detectors D and I),, and impressed upon a signal responsive means herein shown as telephone receivers R1, and R respectively.

Should filters HP and LP not have a sufficiently sharp cut-off to'effectively separate the respective side bands associated with the two channels any undesired components appearing in the output circuits of detectors D and D may be suppressed by low pass filters having a cut-off at 5000 cycles.

In the operation of this system, by selecting the upper side band produced by the lower frequency, i. e., kc., carrier current, and the lower side band produced by the higher frequency, i. e., kc. carrier current, the resultant wave which is used for modulating the high frequency carrier is confined to a 10 kc. range.

Inasmuch as two side bands of the high frequency carrier, i. e., 485 kc., are separated by a frequency range of about kc., one of these side bands may be readily selected by band pass filters from both the carrier and the other side band and used for transmission. This wave will have a fre uency range of 10 kc., which is the same as t at required in a carrier current system in which both side bands'are transmitted. This is a desirable requirement for transmission systems in general in order that the maximum number of communication channels may be employed within a given frequency band.

In a similar manner, when the components selected by the filters BF and BF are used for transmission over a line the band width of the wave transmitted would be 10 kc.

In order to facilitate the selection at the receivin station of the lower frequency signal mo ulated waves, the carrier oscillations, supplied by the oscillators O and 0,, may be chosen to provide the desired frequency interval between the upper limiting frequency of one wave, and the lower limitingfrequency of the other wave.

Although a particular system has been disclosed and a particular manner of operation set forth in connection with this invention, it is notto be limited thereto but only in accordance with the scope of the inven 1 0 ated so as to register different versions of the sounds to be transmitted, sources of con.-

to modulate separately each of said waves in accordance wit the sounds from a different one of said two pickup elements, means as'-' sociated with each modulating means for tinuous waves of different frequency, means selectively transmitting one of the resulting side bands while suppressing the opposite side band, the frequencies of said continuous Waves being separated in the frequency spectrum by a proper interval depending on the frequency range of the sounds from said pick-up elements, and the proper side bands being selected, to cause said two selected side bands to occupy substantially the same total frequency range as the range from one of said pick-up elements added to that from the other, and means for transmitting over the same path to a distant point for separate reception thereat the frequency components contained in the two'selected side bands.

2. A system as defined in claim 1 in which the means for transmitting to a distant point the frequency components contained in the two side bands comprises means for modulating a radio wave by-said two side bands and for suppressin one of the resulting radio frequency side ands while transmitting the other, the fre uencies of said two continuous waves whic the two sound versions modulate being sufficiently high with respect to the radio wave frequency to enable one radio frequency side band to be effectively separated from the other by filtering only.

3. A system as defined in claim 1 in which the means for selecting the side bands for transmission comprises means for selecting the upper side band resulting from the modulation of the lower frequency one of the two continuous waves and means for selecting the lower side band resulting from the modulation of the higher frequency one of the two continuous waves.

4. A receiving system for the system defined in claim 1, comprising a pair of selective circuits for separating the two side bands, a detector for each side band, and a receiver element individually associated with the output of each detector.

5. A binaural transmission system comprising two sound pick-up elements operatively related to a source of sound means to generate two continuous waves of different frequency each high in comparison with any sound frequency to be transmitted, means to modulate the lower frequency continuous wave in accordance with sounds from one pick-up element, filter means to suppress the resulting lower side band but transmit the continuous wave frequency and the upper side band, means to modulate the other continuous wave in accordance with sound from the other pick-up element, filter means to suppress the resulting upper side band but to transmit the continuous wave and the lower side band, the frequencies of said continuous waves being separated such a distance in the frequency spectrum that the two selected side bands form practically a continuous range of frequency components, means to transmit such frequency components and reproduce them at a distant point, filter means thereat for selecting to different circuits the two continuous wave frequencies and the respective side bands based thereon, detector means in each circuit for reproducing in separate circuits components corresponding to the sounds from the respective pick-up elements, and a separate receiver element associated with each of said latter circuits.

In witness whereof, I hereunto subscribe m g name this 10th day of December, A. D. 19 5.

JOSEPH W. HORTON. 

